About that 750 ohms. The input transformer has a three-to-one voltage step up, which gets us a nine-to-one impedance step up. Should translate to 450 ohms, not 750. I use four 470 ohm resistors, two series pairs in parallel. I'ts an overkill thing. Joe CBer may overdrive his Pride, but the new swamping resistors won't suffer. Other stuff will. Gets me the equivalent resistance of a single part that value. The factory's two original 1.5k 2-Watt resistors routinely overheat. Not sure what the designer was thinking with that 750 ohm value, except maybe to get a bit more drive to the tube grids than a proper 450 ohm swamping resistor value would do. Don't see just how that makes sense, since it's exquisitely easy to overdrive even with a swamping resistor closer to 450 ohms.
A T network does serve to bring the input match closer to 50 ohms in the DX300. The T attenuator will minimize any mismatch in the tube's grid circuit impedance. Whatever the input SWR was before, the T attenuator will tend to reduce it.
There's more than one way to skin a cat. We tried using a two-to-one input tranformer ratio with a 200 ohm swamping resistor in a Pride. Took too much drive power to achieve the signal voltage needed on the control grid. The T network with a three-to-one transformer provided a better "middle ground" appropriate to a customer's "two-final" black base radio.
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